This application uses a previously known method called the Wallace spacing loss equations as found in U.S. Pat. No. 5,130,866, issued in 1992 to estimate flying height clearance, given a predetermined pattern being read with a recording wavelength of λ of the first harmonic, with the first harmonic amplitude at flying state a being Aa-1st and the kth harmonic amplitude at flying state a being Aa-kth. The spacing change Δd between flying state a and flying state b is given in terms of the ratios of first and third harmonics asΔd=(λ/4π)ln(Aa-1stAb-3rd/Ab-1stAa-3rd)  (1)
This spacing change may also be calculated based upon a single tone byΔd=(λ/4π)ln(Aa-1st/Ab-1st)  (2)